Conventional paintbrushes include bristles which are attached to a handle. The bristles are typically inserted into a metal head and after gluing the head is attached to a handle with staples if plastic and nails if wood. This has to be done carefully using a handle and metal head that have precise measurements to prevent a loose fit. Some manufacturers prefer plastic or composite handles because unlike wood they do not shrink or expand due to humidity or dryness. A major challenge in manufacturing a paintbrush is attaching the head of the brush (that part which contains the bristles) securely to the handle, regardless of whether the handle is plastic or wood. Heat or moisture can cause shrinkage or swelling and this creates a loose fit and annoying movement while the user is painting brush strokes.
To mitigate the above-cited problems, some paintbrush designs include a replaceable head which removably connects to the handle. This concept of a standardized design facilitates head manufacture, and also allows the handle to be reused with multiple heads.